A ligament is a piece of soft, fibrous tissue that connects one bone to another bone in the skeletal system. Ligaments can often become damaged or injured. When damaged or injured, ligaments may tear, rupture or become detached from bone. The loss of a ligament can cause instability, pain and eventually increased wear on joint surfaces, which can lead to osteoarthritis.
Various surgical techniques have been developed for ligament repair. The particular surgical technique used depends on the ligament that has been damaged and the extent of the injury.
One ligament which is commonly injured is the anterior cruciate ligament (ACL). As seen in FIG. 1, the ACL 5 extends from the top of the tibia 10 to the side of the notch 15 which is located between the femoral condyles 20 of the femur 25.
Trauma to the knee can cause injury to the ACL. The ACL may become partially or completely torn. FIG. 2 is a schematic view showing a torn ACL 5 in the left knee. An intact posterior cruciate ligament (PCL) 30 is shown behind the torn ACL 5.
A torn ACL reduces the stability of the knee joint and can result in pain, instability and excessive wear on the cartilage surfaces of the knee, eventually resulting in osteoarthritis.
Several approaches are available for ACL reconstruction. One of the most commonly used ACL reconstruction techniques involves removal of most, or all, of the torn ACL, drilling bone tunnels in both the femur and the tibia, inserting a tissue graft (sometimes referred to herein as simply “the graft”) into the tibial and femoral tunnels so that the tissue graft extends across the interior of the knee joint in place of the native ACL, and securing the tissue graft in the femoral and tibial tunnels with interference screws or other fixation devices, so that the graft extends from the top of the tibia to the side of the femoral notch.
More particularly, and looking now at FIG. 3, an aiming instrument 35 is aligned to tibia 10 and a tibial guide pin 40 (for guiding a cannulated drill, see below) is drilled into tibia 10. FIG. 3 illustrates a typical aiming instrument 35 for targeting the tibial guide pin 40 from the outside of tibia 10 to an exit point 45 on the tibial plateau 50 at the location corresponding to the insertion point of the natural ACL. Note that tibial guide pin 40 enters tibia 10 at an angle α relative to the plane of tibial plateau 50, and exits the tibial plateau at the same angle α (relative to the plane of the tibial plateau).
After tibial guide pin 40 has been appropriately drilled through the tibia, aiming instrument 35 is removed from the tibia, leaving tibial guide pin 40 in place. As seen in FIG. 4, a cannulated drill 55 (i.e., a drill with a center hole extending along the length of the drill) is slid over tibial guide pin 40 and drilled from the anteromedial surface of tibia 10, through the tibia and into the joint space 60 of the knee. FIG. 4 shows tibial guide pin 40 and cannulated drill 55 after cannulated drill 55 has been drilled through tibia 10. In this way a tibial tunnel 70 may be formed in tibia 10, with the tibial tunnel extending from the anteromedial surface of the tibia to the insertion point of the native ACL on the tibial plateau.
A similar process may be followed for drilling into femur 25, i.e., a femoral guide pin 65 may be inserted through tibial tunnel 70 and into femur 25 as shown in FIG. 5, and then a cannulated drill 75 may be drilled over the femoral guide pin 65 and into femur 25. In this way a femoral tunnel 80 may be formed in femur 25, with the femoral tunnel extending from the side of the femoral notch to part or all the way through the femur. Ideally, the joint-side mouth of femoral tunnel 80 is located at the insertion point of the native ACL on the femoral notch.
The method described above and shown in FIG. 5 is sometimes referred to as “transtibial femoral tunnel drilling”, since femoral tunnel 80 is drilled using access through tibial tunnel 70. One problem with transtibial femoral tunnel drilling is that the location of the joint-side mouth of femoral tunnel 80 typically ends up being higher in the femoral notch 15 than the insertion point of the natural ACL, because access to the femur is limited by the location and size of tibial tunnel 70.
On account of the foregoing, an alternative method has been developed to create femoral tunnel 80, i.e., by drilling the femoral tunnel using access through the “accessory medial portal”. More particularly, accessory medial portal drilling of the femoral tunnel involves drilling across the knee joint through a medial portal skin incision 85 such that the joint-side mouth of femoral tunnel 80 can be placed in a more anatomic position. In accessory medial portal drilling, and looking now at FIG. 6, femoral guide pin 65 is first passed through medial portal skin incision 85 and is then drilled into the desired anatomic location on the femur (i.e., the insertion point of the natural ACL on the femur). Then a cannulated drill 75 is slid over femoral guide pin 65 and drilled into femur 25 so as to form femoral tunnel 80. Thus, femoral guide pin 65 and cannulated drill 75 enter through medial portal skin incision 85 and traverse across joint space 60 to the side of the femoral notch. As seen in FIG. 6, femoral guide pin 65 and cannulated drill 75 must enter in front of the adjacent femoral condyle 20 in order to prevent damaging the condyle. The knee quite often must be put into a state of deep flexion in order to reach the desired location (i.e., the insertion point of the natural ACL on the femur) and safely pass by the adjacent condyle 20 and tibial plateau 50.
Accessory medial portal drilling is generally considered to represent an improvement over transtibial femoral tunnel drilling in the sense that it can be used to create a more anatomic ACL reconstruction.
After tibial tunnel 70 and femoral tunnel 80 have been created, the tissue graft is prepared. The tissue graft is typically harvested from the patient's own body tissue and may comprise hamstring tendons, quadriceps tendons, and/or patellar tendons. Alternatively, similar tissue grafts may be harvested from a donor and also include Achilles tendons, anterior tibialis tendons or other graft sources. Looking now at FIG. 7, a tissue graft 90 is prepared by creating one or more long tissue graft strands or graft bundles 95, folding the graft over onto itself so as to create a folded section or loop 100, and making measurements along the graft. Example measurements for adults are 30 mm of graft length for the portion of the graft that is to be inserted into femoral tunnel 80, 27 mm to 30 mm for the portion of the graft that is intra-articular (i.e., inside the knee joint 60) and 35 mm for the portion that is to be positioned inside tibial tunnel 70. FIG. 7 shows tissue graft 90 folded over into two graft bundles 95 and a folded section or loop 100, and the corresponding graft measurements. Sutures (whipstitches) are typically applied at the areas of the graft that will interface with the femoral and tibial tunnels so as to add additional strength to the tissue graft. As will hereinafter be discussed, the folded section or loop 100 of tissue graft 90 will interface with femoral tunnel 80 and the two opposite ends (i.e., portion of graft bundles 95) will be disposed in tibial tunnel 70.
As seen in FIGS. 7 and 8, graft tow sutures 105 are looped around the folded portion or loop 100 of graft 90, forming a strand of sutures that can be used to pull graft 90 into place. More particularly, the free ends of graft tow sutures 105 are passed through tibial tunnel 70 and femoral tunnel 80, e.g., with the assistance of a suture passing guide wire (not shown) of the sort well known in the art. Once the free ends of graft tow sutures 105 have been passed through the tibial and femoral tunnels, the free ends of graft tow sutures 105 can be pulled so as to pull graft 90 into the tibial and femoral tunnels. FIG. 8 shows graft 90 folded over and in position to be pulled through tibial tunnel 70 and into femoral tunnel 80 using graft tow sutures 105. The graft tow sutures 105 emanating from the distal end of femoral tunnel 80 are grasped with a clamp 110, and clamp 110 and graft tow sutures 105 are used to pull graft 90 through tibial tunnel 70, across the interior of the knee joint, and into femoral tunnel 80.
Once tissue graft 90 is in place, the individual graft bundles 95 making up the aggregate tissue graft 90 may be manipulated to approximate the anatomic positions of the native ACL.
Advances in the research of ACL anatomy indicate that there are two primary bundles that make up the natural ACL, the anteromedial bundle and the posterolateral bundle. More particularly, and looking now at FIG. 9, the anteromedial bundle 115 and the posterolateral bundle 120 are also referred to as the “AM” bundle and the “PL” bundle. The particular name of the ligament bundle refers to its point of origin on tibial plateau 50, i.e., AM bundle 115 originates anteromedially and PL bundle 120 originates posterolaterally (relative to each other on the tibial plateau). As seen in FIG. 9, the AM and PL bundles are roughly parallel to each other when the knee is in full extension.
However, when the knee is fully flexed, and looking now at FIG. 10, AM bundle 115 and PL bundle 120 “cross” each other. As such, a true anatomic reconstruction of the ACL must place the graft bundles 95 into the proper femoral and tibial positions in order to achieve the natural kinematic motion of the ACL and the knee joint.
Thus, in an ACL reconstruction, it is desired to manipulate graft 90 into position such that the two graft bundles 95 (see FIGS. 7 and 8) making up the aggregate tissue graft 90 are located in the approximate positions of the natural AM and PL bundles of the native ACL. It has been demonstrated in biomechanical tests that this construct results in a more stable ACL reconstruction.
After graft 90 is inserted into the tibial and femoral tunnels, preferably with graft bundles 95 disposed so as to mimic the natural AM and PL bundles of the native ACL, fixation screws (also known as interference screws) are inserted into the femoral and tibial bone tunnels so as to secure graft 90 to femur 25 and tibia 10. More particularly, and looking now at FIG. 11, the femoral portion of graft 90 is first fixed into place by inserting a femoral interference screw 125 through the medial portal skin incision 85, advancing femoral interference screw 125 across the interior of the joint, and then screwing femoral interference screw 125 into femoral tunnel 80 e.g., with a driver 127. Femoral interference screw 125 squeezes graft 90 tightly against the wall of femoral tunnel 80. As femoral interference screw 125 is tightened into place, the femoral interference screw creates an interference fit between femoral tunnel 80, graft 90 and femoral interference screw 125.
FIG. 12 shows the femoral fixation in place, with AM bundle 95AM of graft 90 approximating the anatomic position of the native AM bundle and PL bundle 95PL of graft 90 approximating the anatomic position of the native PL bundle.
Finally, and looking now at FIG. 13, a tibial interference screw 130 is screwed into tibial tunnel 70 so as to secure graft 90 in tibial tunnel 70.
The foregoing technique has been used for many years for the reconstruction of a damaged or injured ACL. This technique has generally been successful, but it does have some limitations. Typically, the location of graft 90 around the perimeter of interference screws 125, 130 is uncontrolled because the graft bundles 95 rotate as the interference screws are inserted. As a result, it is difficult to set the interference screws while keeping AM bundle 95AM and PL bundle 95PL in their correct anatomical positions.
Furthermore, on the tibial side, tibial interference screw 130 may skive off the centerline of tibial tunnel 70 as tibial interference screw 130 is screwed into place. As a result, the AM and PL bundles 95AM, 95PL may bunch up and migrate to one side of tibial tunnel 70. This occurrence creates a non-anatomic reconstruction which may also result in reduced pull-out strength and can contribute to changes in the natural motion of the knee. Clinically, this occurrence may contribute to tunnel widening where the tibial interference screw 130 skives off to one side of the tibial tunnel and the AM and PL bundles 95AM, 95PL are bunched up on the other side of the tibial tunnel, causing the softer cancellous bone inside the tibia to collapse. FIG. 14 illustrates how the off-center disposition of tibial interference screw 130 can result in a non-anatomic reconstruction: the AM and PL bundles 95AM, 95PL may not be located in their correct anatomic positions; at various degrees of knee flexion, one of the bundles may become excessively slack; the overall strength of the construct may be reduced; and natural knee motion may be altered, contributing to the development of osteoarthritis or an increase in the need for subsequent revision surgery.
A closer analysis of how the tibial and femoral tunnels 70, 80 are formed, and a closer look at the anatomic insertions of graft 90 into the femur and tibia, illustrate how graft fixation can be configured to produce a more anatomic reconstruction.
Because cannulated drill 75 enters the surface of femur 25 at an angle (FIGS. 5 and 6), the entrance of femoral tunnel 80 is elliptical (FIG. 15). This elliptical shape is not due to poorly manufactured drills, poor surgical technique, etc. It is the normal result of drilling a hole into a surface while the drill is set at a non-perpendicular angle to the surface. This is illustrated in FIG. 15, which shows the outline of femoral tunnel 80 when looking directly into the bone surface.
Similarly, when cannulated drill 55 exits tibial tunnel 70 and enters the interior of the joint at an angle (FIG. 4), the shape of the tunnel opening is elliptical at the tibial plateau 50 (FIG. 16).
This elliptical shape of the joint-side entrance of femoral tunnel 80 and at the joint-side exit of tibial tunnel 70 has been documented in biomechanical studies.
For reference, the normal anatomic ACL insertion shape, or morphology, on the surface of the femur is shown in FIG. 17. The AM and PL bundles 115, 120 are shown in typical anatomic locations.
Similarly, the normal anatomic ACL insertion shape on the surface of the tibia are shown in FIG. 18. The AM and PL bundles 115, 120 are shown in typical anatomic locations.
Typical interference screws fixate graft 90 along the length of the interference screws, with the graft located between the interference screw and the side wall of the bone tunnel. See FIG. 19, which shows femoral interference screw 125 securing graft 90 to femur 25. However, as discussed above and as shown in FIG. 14, the two graft bundles 95 of graft 90 do not typically lie in the true anatomic AM and PL bundle locations because graft bundles 95 rotate with the rotation of the interference screws before coming to rest in their final fixed position.
In a similar fashion, graft bundles 95 may rotate or be compressed into non-anatomic positions at the entrance of tibial tunnel 70.
In addition, with respect to tibial fixation, the curved taper at the tip of an interference screw lies near the joint-side exit of tibial tunnel 70, and this distal taper of the interference screw creates some laxity of graft 90. FIG. 20 shows the AM graft bundle 95AM and the PL graft bundle 95PL shown approximately in their anatomic positions. The area at the distal end of interference screw 130 shows how graft 90 is loosely fixated in the area near the distal tip of the interference screw. This loose fixation of graft 90 may contribute to problems such as the so-called “windshield wiper effect”, where graft 90 sweeps across the opening of the bone tunnel, thereby causing abrasion to the graft and to the bone tunnel; and joint laxity due to incomplete fixation of the graft into its anatomic position.
Thus there are problems with standard interference screw fixation: the graft bundles may come to rest around the interference screw in non-anatomic locations, resulting in a biomechanical construct that does not replicate the native anatomy; there is a lack of complete fixation of the graft at the opening of the bone tunnel to the joint space; and the unsecured graft in the elliptical opening of the bone tunnel may contribute to the windshield wiper effect, biomechanical instability and tunnel widening.
Another type of graft fixation in common use is sometimes referred to as suspensory fixation. In suspensory fixation, and looking now at FIG. 21, graft 90 is passed through a fabric loop 135 which is, in turn, secured to a button 140. Button 140, loop 135 and graft 90 are inserted into a femoral bone tunnel 80, and button 140 is “flipped” outside the distal bone cortex so as to suspend the graft in the femoral tunnel. In one variation of this technique, and as is shown in FIG. 21, anatomic reconstruction is effected by creating two femoral bone tunnels 80, one for the AM bundle 95AM and one for the PL bundle 95PL.
As also seen in FIG. 21, a similar approach may be used on the tibial side.
Furthermore, if desired, and as is also shown in FIG. 21, an interference screw 142 may also be used to enhance femoral or tibial fixation.
In this type of ligament reconstruction, the grafts 90 are freely suspended in the femoral tunnel(s) 80. Micro-movement of graft 90 due to loading and unloading of the graft tissue may contribute to tunnel widening and loss of fixation. Also, the location of the graft bundles 95 in the femoral tunnel(s) is to some extent uncontrolled, inasmuch as the graft bundles are free to rotate and translate laterally, and to a smaller extent axially, within the femoral tunnel(s).
The previously-described approaches illustrate much of the current practice of ACL reconstruction. Current approaches do not lend themselves to creating a highly accurate anatomic reconstruction. The current devices can result in constructs that do not fully stabilize the graft. The subsequent motion of the graft may contribute to tunnel widening, loss of graft tension, loss of knee stability and may result in the need for subsequent revision surgery.